Method and apparatus for countercurrent contacting of liquids



Jan. 25, 1949. J. D. LONG ET AL 2,460,019

METHOD AND APPARATUS FOR COUNTER-CURRENT CONTACTING OF LIQUIDS Filed Aug. 23, 1944 s Sheets-Sheet 1 I 1') H In Inventors Clbborneq Jan. 25, 19 49. J LONG ET AL 2,460,019

METHOD AND APPARATUS FOR COUNTER-CURRENT CONTACTING OF LIQUIDS Filed Aug. 25, 1944 3 Sheets-Sheet 2 VATHS OF THE 5 ConTmuousPmse FIG-2a UnvenborS Jan. 25, 1949. J LONGER AL 2,460,019 METHOD AND APPARATUS FOR COUNTER-CURRENT CONTACTING OF LIQUIDS Filed Aug. 23, 1944 3 Sheets-Sheet 3 FIG-5a Ubhn D. Lonq Cum! 0. Rh J 3nventors Patented Jan. 25, 1949 ME'EEOD AND AiPARATUS FQR COUNTER- 6 RR-EN? CGNTACTFNGQF LXQUIDS Eohn D. Long, Westfield, and. Cyril Q. Rhys, Jr.,

Cranford, N. .L, assignors to Standard Oil Development Company, a corporation of Delaware Application August 23, 1944, Serial No. 550,798

8 Claims.

This invention relates to the countercurrent contacting of fluids, and in particular to the countercurrent treatment of substantially immiscible liquids of different gravities.

In the art of intercontacting fluids for refining purposes, many processes have been devised which are dependent in some measure upon-the design of the apparatus employed. It hasbeen found, for example, more advantageousto effect large volume inter-fluid treating, especially liquid-liquid contacting, in towers rather than in mixers and settlers (or centrifuges). Processing in towers has been found more advantage ous from the economic viewpoint because of the lower initial and operating costs, the lower steel requirements and the less groundspace required. Considerable attention has therefore been given to liquid-liquid contacting in towers. It is desirable toachieve high capacity under good .contacting conditions in the towers so that superior product quality and high processing yields-,may be attained. I The efiiciency of treating in the towers depends, therefore, upon the attainmentof good phase contacting without the formation of stabilized emulsions. Of the various towers employed, those involving the use of pierced plates have been particularly advantageous when. large quantities of liquids are involved.

Conventional pierced plate towers consist of a large number of, horizontally disposed perforated plates extending over a large part of the tower area. The plate perforations are small orifices by means of which one of the phases is dispersed.

When the heavier liquid is passed downward through the tower as the discontinuous phase, each plate is provided with risers for the passage upward of the lighter continuous phase and which form a weir or weirs of sufiicient height for the heavier phase to insure a definite head on the plate to effect, by reason of gravity difierential, the dispersion of the heavier liquid into the lighter liquid. The intercontacting of liquids in pierced plate towers under the given flow conditions is thus the dispersion vertically of one phase from the plate orifices into the continuous phase which is moving in an essentially horizontal. direction beneath the plate to reach the location of the nearest weir. Such treating conditions have been found generally satisfactory except in regard to the development of local areas of recycling of the disperse phase especially when the tower is being used alcove a certain capacity, that near flood conditions. Processing. according to .the invention practically eliminates such disadvantages.

The settling rate of the disperse phase in a. conventional pierced plate tower clearly decreases as the throughput and consequently as the velocity of the continuous phase increases. As, a result therefore of conventional pierced plate tower operation, the disperse phase issuing iromthe orifices nearest to the weirs may be carried into the adjacent settling zone by means of the horizontally moving stream of the continuous phase and then recycled to the plate from which such portions of the disperse phase had previously come. Furthermore, this tendency towards recycling increases as the throughput of the continuous phase increases. Thus, as the flow of the continuous phase over such pierced plates is increased beyond. a certain value, the particularly advantageous capacity of the tower, correspondingly poorer and poorer treating efffects are obtained,

Inan effort to modify the conventional pierced plate towertofavoid recycling, it was found that by blankingthe orifices on the side of the plates nearest to theweir or weirs an improvement in contacting conditions was obtained. It was further found that by moving the weirs back to a point close to the pierced section and building the plate in the form of. two steps with the 'weir as a riser and the spacing of the plates widely apart a further improvement could be attained. This change also involved a ch nge in the settling conditions from that of settling from horizontally movingstreams of the continuous phase to settlingfrom substantially vertically moving countercurrent streams. From a contacting as well as froma settling viewpoint,-v this change was found advantageous. Thus, the plates in the tower could be spaced further apart and on. the plates narrow and deeper troughs could be .constructed, thereby permitting a higher head than previously of the phase to be dispersed.

According to these principles, as the basis of the prcsentinvention, an embodiment or illustration of the invention may be taken in the design of a particular treating tower. In this tower the 3 design involves having a series of plates containing troughs for the collection of the heavier discontinuous phase. These troughs have their bases drilled with holes through which the phase which collects therein becomes dispersed into the space below, particularly by reason of the liquid 7 determines the extent of the liquid head necessary to force the phase to be dispersed through the holes in the bases. The droplets which are sprayed from the holes in the troughs are moreover settled through a zone in which the lighter phase has to flow in an essentially vertical direction. The droplets of the heavier phase coalesce on the top of the next lower plate and then fiow into the trough or troughs in that plate. The lighter phase passes upwards in the tower through the plate openings.

In a tower of such design, as the velocity of the continuous phase moving in a substantially vertical direction increases, the settling rate of the discontinuous phase therein decreases, and at a certain maximum velocity of the discontinuous phase the majority of the droplets will no longer settle but will be entrained along with the continuous phase; that is. the point of flooding of the tower. Such processing is thus in' marked contrast to that which normally occurs in the conventional type pierced plate towers. Moreover, as the throughput in towers designed according to the present invention increases, the entrainment does not become progressively greater until flooding occurs provided that droplets of relatively uniform size are produced. Moreover, as the throughput in such towers increases, the amount of time available for each droplet in the settling zone increases, thus conveying improvement in treating efficiency. 7

In such an'apparatus, any degree of contacting may be obtained by varying the size and number of the holes in the troughs, and, since the size of the droplet determines the settling rate 4 sure drop across the orifices. The latter two can be varied at will regardless of the type of plate construction, although from practical consideration the vertical type controller is more advantageous with higher pressure drop thanwith the conventional pierced plate type. As regards the time available for diflusion, settling from substantially countercurrent vertically moving streams has, as previously pointed out.

distinct advantages over settling from horizontally moving streams. droplets of the disperse phase can pass through horizontally moving streams of the continuous phase when the velocity is relatively high, the

droplets of smaller size being subject to the carrying power of the continuous phase and thus to i recycling. Thus, in the conventional pierced plate tower, as the maximum capacity is reached plate efficiency falls ofi sharply due to recycling and to the rapid passage of only large droplets through the continuous phase. On the; other hand, in towers designed according to the present invention, as the tower approaches maximum capacity the time of contacting for all droplets increases and hence the plate efiiciency also tends to approach a This is of great importance for reasons of economy since it is always desirable to operate towers at the maximum rates.

The invention may be specifically illustrated by the processing effected in an apparatus diagrammatically' illustrated in Figures 1a, 1b, 1c and 111. Figure la represents a section of a tower l0 according to the invention containing two plates 2E! and 30, respectively. Figures 1b and 1c reppierced plate tower.

of the discontinuous phase, the rate of settling V in the discontinuous phase is also controlled. The diameter of such a tower necessarily becomes dependent upon the flow rates and degree of contacting required, while the height of the tower will be determined by the number of plates required for the extraction operation; the latter also being determined by the number of theoretical extraction stages required and the plate efficiency.

In order to understand more clearly the advantages of processing according to the invention and the improved plate eificiency'also involved, the mechanism of material transfer in liquid-liquid contacting systems will be further analyzed. In the contacting of the two phases, one of the most important'features in the interchange of soluble constituents is the range of distribution coefficients of the various solutes between the various solvents. Plate efficiency is dependent also upon a number of variables. These variables include the solute concentration differential between the liquid phase, the rates of diffusion of the solutes in each phase, the size of the droplets and the time available for difiusion. Ofthese variables, only the latter two are subject to control'by tower design. The size of the droplets is mainly a functional interfacial tension, orifice size and presresent plan Views of the plates shown in Figure 1a. Figure lid represents a cutaway section of the tower showing the same two plates. Figures 2aand 2b show the fiow of fluids according to processing of the invention and in a conventional Figures 3 and 4 represent other modifications of the invention.

As shown in Figures 1a and lb, plate 20 consists of an inverted trough 2| extending across'the 7 center of the tower and two symmetrical 'flat horizontal plates 22 and 23 extending in both di rections from the trough edges almost to the shell of the tower. edges of the plate and the shell of the tower Ill serve as passageways for the flow of the continuous phase. The trough M has angle sides 26 and 2! and may be capped by'th'e horizontal plate 28. The angle sides 26 and 2'3 are perforated to 7 act as orifices for producing droplets of the phase to be dispersed. The plate 31) is positioned directly below the plate 20 as shown in Figure 1a and consists of two short inverted troughs 3i and '32 and two fiat plates 33 and 34 extending from the trough edges almost to the center line of the tower as shown in Figures 1a and 1c. The space 35 thus formed acts as a passageway for the flow of the continuous phase. The troughs are provided with angle sides 36 and 31 for ejecting the phase to be dispersed.

It is apparent that by alternating plates of the type 20 with those of 30 in the tower the continuous phase will be caused to flow downward and contact droplets of the discontinuous phase flow-. ing upward from the inverted troughs. Such processing is indicated in Figure 2a and contrasted with the contacting occurring according to processing in a conventional pierced plate Y tower," Figurezb. v j f It should be understood that a multiplicitypf inverted troughs may be used on each plate as shown-in Figures 3a and 3b rather than one or Also, only the largest The spaces 24 and 25 between the .two as .fdescribedzabove.

anemone Plates 548 and iii! Lbfll' structural rrelationships to :plates 12%) sand I 30 'gof :Figure;.1. .flhe inverted.troughs M have-angle perforated sides :45 which may be capped :by :horifZOIlilEtl'j plates '46. The-inverted troughs have at their? bases .fiatrhcrizontalg-plates -42: and: 43 which inlthiscase rddnotzextendalmost across the diam- .eter-"ofxthe shell jofthe-tourer 'tii-butmerel-yi por-- .tions of ;,the amount determined by the :number "of troughs ,on the plate. Between the various .troughplate assemblies are the spaces 44 .serving asrpassageways for the flow of 'the .continuous :phase. vThe plate 58 isshown-as'being a com- ..positeqoi plates of theitype 2B and 130 as shown in 1 Figure 1. shell has-the inverted trough portions and 52 .with perforated angle sidesrtfi andziil tslmilar=.to .the corresponding.portions orthe inverted troughs 3i and 32 of plate 39. Furthermore, the shape of the troughs mayhe .varied as. for Figures -;4a, 4.-b,andlcyviithin the concept of the invention provided that the means thereby afiorded for the set-tling of the discontinuous phase ly Washed hydrocarbon stream Concentration of acetonein "infthe continuous "phase is through a vertical 'stream of the "continuous phase rather than 'a lrorizogntall-y flowing *stream.

ilrocessing according to the invention involving the-use of theabove typeapparatus requires that the heavier of the the top of =thetower whilethe lighter component is introduced .at therbottom. nsiindicated by the arrows in Figures 1, 2a, 3 and .4 the lighter phase is ,processed in the tower by passing through the :orifices 'inthe inverted troughs :and thence by settling -through "the continuous, substantially vertically moving streams of the continuous phase. The lighter phase then collects on the under side of the various plates such as plate and is trans ferred to the trough such as 2i from which the liquid again emerges as droplets to be contacted again by the continuous phase. Such operation is repeated until the lighter phase reaches the top of the tower and the heavier phase reaches the bottom of the tower. In this manner, intimate contact within the two phases is attained and adequate settling assured.

The direction of flow of the two streams is immaterial according to the invention, although in the above description it has been assumed that the continuous phase passes downward and the discontinuous phase flows upward.

As a specific illustration of processing according to the invention, the treatment with water of the hydrocarbon stream from an extractive distillation system to remove solvent soluble in water may be employed. Thus, in the extractive distillation of the C4 and C5 hydrocarbons with aqueous acetone as the solvent, the acetone has to be recovered in the interests of economy from the various streams. For such an example, to a tower design as illustrated in Figure 1, may be taken the removing of acetone from the predominantly butane stream from an extractive distillation unit employing aqueous acetone as the solvent. Such a stream usually contains about 10% acetone. The data from a ternary diagram for the system--water, acetone and butaneand a stage-to-stage calculation indicate that seven theoretical stages are required when using an eco- Theportion-of the platenear the example, in

two liquids be introduced at weight per cent. 0.01

. rality of alternate 'locity, the said change oi-velocity being obtained about 13.05% .:and to Ehavesabout ;13.

the diagram by theznumeralzi -31). "The average head in inomical quantity of wasir-avaterto reduceitheiconinthe butane :stream :to

-.concentra'- tion of acetone in the'waterwash stream. Such processing hasheen satisfactorily effectedaccoiiding to the invention by..employingsan-tower (iii-:5 feet. in "diameter and. -iieetl inrhei'ght: containing centration of acetone .30 plates'of the typeshownin:Figurellvspacdd 2 /2 feetrapart.

.The troughs are :of :two :types: relatively long inverted troughs .as.:designated in which :have .1242 /4111011 :holes, and relatively short inverted troughs such as designated by the 'numeraL-SI having. 122 A a-inch holes per troughrorfiathiiles per plateof .the type; designated by .the numeral the invertedatroughs his between. 10 and 12 inches. Under suchsconditions .a 5d to "75%v spray ofaverage'size droplet of of an inch is. obtained. The settling zones were designed. to allow adequate settling of the droplets as smallias trof an inch inidiameter.

Data-obtained by processing in such a tower are as follows:

Tablel 7, 6, 515 0, 880 5.950 6,900 s,- 900 .4, 005 4, 005 4, 005 4. 005 4, 005 14, 005 4; 940 4, 355 5, 710 5; e45 5,1570 7 5, can 0. 01 0. 00s 0. 0 0. c1 7 0.0 0.0

What is claimed. is: v 1. A process for countercurrent-ly contacting relatively immiscible fluidsoi different gravities, comprising passing "a continuous stream of one fluid througha systemcontainin aseries ioicontact zones, each of said zones containing'a-pluregions oi high'and low veby alternately constricting and enlarging the stream asit iiowsthrough the system passingt'he other fluid as a discontinuousphase in'tlie oppo site direction, injectingthe said other 'flui'd 'a finely divided state into the high velocity regions of the stream of the said first fluid, allowing the mixed fluids to separate by gravity in the low velocity regions, passing the thus separated fluids in opposite directions for further contact in the successive contact zones, and withdrawing the separated fluids respectively from opposite sides of said system.

2. A process as in claim 1, in which both fluids are liquids.

3. A process as in claim 1, in which the respective fluids are contacted by intersection substantially at right angles in the high velocity zones.

4. A process as in claim 1, wherein the said discontinuous phase is dispersed to form fine portions by being forced through small orifices by gravity differentials.

5. A process as in claim 1, wherein the separation of the two phases by settling occurs in regions where the path of the continuous stream has a relatively large cross-section.

6. An apparatus for the countercurrent treatment of relatively gravity, comprising an upright shell fitted with a plurality of transverse plate assemblies which subdivide the interior of said shell into a series of settling chambers, each assembly comprising at least one narrow inverted trough, adapted to collost an ascending fluid of relatively light gravity, the trough having its open end edges flanged by horizontally disposed base portions extending outwardly from the trough edges each said base portion having at least one constricted opening for permitting the downward flow of a fluid of immiscible fluids of different '7 relatively heavy gravity, the trough being fitted in its upper solid portion with small perforations adapted to disperse the ascending fluid, alternate assemblies having said troughs and said constricted openings alternately disposed, said troughs of one assembly terminating in spaced relation to said constricted openings of the next higher assemblyto cause the ascending fluid to intercept the descending fluid at a point of substantially most rapid flow of said descending fluid as it pa-ssesthrough said constricted opening, and an inlet and an outlet in both the uppermost and the lowermost settling chamber.

7. An apparatus for countercurrent extraction of fluids comprising an upright shell, a plurality of transverse bafile assemblies dividing the interior of the shell into a series of settling chambers, each assembly formed of a horizontally disposed base containing at least one constricted slot extending transversely of the base and adapted to permit downward flow of a relatively heavy liquid in a constricted stream, a portion of said base formed into at least one inverted U-shape portion which extends upwardly from the horizontal base portion and is aligned in spaced relation to ,aconstricted slot of .the ,fsuch tJ'j-shape portion being; fitted near, its crest "with perforations adapted liquid as it tling chambers, one type of said plates consisting of a narrow inverted trough at least 10 inches deep extending across a diameter of the shell, the upper solid portion of said trough fitted with fine perforations next higher. assembly;

tq disp rse a relatively, I light liquid in a finely divided state into a rapidly 4 inch in diameter adapted to dis perse a relatively light fluid, the open end of each inverted trough flanged with two symmetrical horizontal plates extending in both directions from the trough edges and terminating in spaced relation to they shell, thus forming a constricted passageway .for a descending relatively heavy fluid, the alternate-type of plate consisting of a horizontally-disposedbase having a constricted slot extending transversely of the base and aligned with the inverted trough of the next lower plate, said base terminating on opposite sides in edges spaced from the wall and havin an upwardly extending flange on each said edge, the upper portion of each flange terminating in a wall which is inclined and extends to meet the shell, the inclined wall being fitted with small perforations; the shell also comprising an inlet and an outlet in both the uppermost and the lowermost settling chamber.

' JOHN D. LONG.

CYRIL O. RHYS, JR.

REFERENCES CITED The following references are of record in the his of this patent:

Number: -="'Name- Date 1,170,658 Mitchell Feb. 8, 1916 1,320,396 Laird Nov, 4, 1919 1,621,728 Jordan Mar. 22, 1927 1,782,735 Mackenzie Nov. 25, 1930 2,009,510 Mobley July 30, 1935 2,144,797 Dons etral Jan. 24, 1939 2,153,507 Mann Apr. 4, 1939 2,274,030 Atkins Feb. 24, 1942 FOREIGN PATENTS Number Country Date 156,490 Great Britain Jan. 5, 1921 199,345 Germany Dec. 17, 1907 

